// 提供各种混合

.sel-center(@position:absolute) {
  position: @position;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

.self-fill(@position: absolute) {
  position: @position;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
}